Semiconductor memory devices may be classified into volatile memory devices and non-volatile memory devices. In the case of the volatile memory devices, all stored data may be lost if the power supply is shut off.
Dynamic random access memory devices (DRAM devices) and static RAM devices (SRAM devices) are representative volatile memory devices.
In the case of the non-volatile memory devices, even if the power supply is shut off, stored data are retained. Due to such a characteristic, the non-volatile memory devices may be used as storage media installed in potable appliances and/or electronic appliances. NAND flash memory devices among the non-volatile memory devices have been extensively used as storage devices of electronic appliances, such as smart phones, digital cameras, and solid state drives (SSDs).
As semiconductor industries have been highly developed, various characteristics of non-volatile memory devices may be improved. For example, data stored in non-volatile memory devices may be lost due to several external causes and/or several internal causes. The data loss may be one cause of significantly serious errors in non-volatile memory devices. Recently, many studies and research have been carried out to improve several characteristics of non-volatile memory devices according to the demand of highly-advanced semiconductor industries.